1. Field of the Invention
The present invention relates to surface emitting devices and liquid crystal display (LCD) apparatuses. In particular, it relates to a bonding structure between a light source and a light guide bar in a surface emitting device for ensuring efficient use of light emerging from the light source.
2. Description of the Related Art
Some LCD apparatuses, for example, reflective LCD apparatuses, require reflection of ambient light for display. In such LCD apparatuses, those having surface emitting devices (front lights) on the front sides have been developed in order that they can be used in dark places where the ambient light is insufficient (for example, see Japanese Unexamined Patent Application Publication No. 2002-140913).
FIG. 9 is an external perspective view showing an LCD apparatus having a surface emitting-device. As shown in FIG. 9, a surface emitting device 110 is disposed on the front side (upper side) of a liquid crystal panel 120 such that the liquid crystal panel 120 is illuminated from the front. A light guide plate 112, a light guide bar 113, and a light source 115 constitute the main part of the surface emitting device 110.
The light source 115 is integrated with the light guide bar 113 disposed along an edge of the light guide plate 112 and serves as an extended light source that emits a wide beam of light toward a side surface of the light guide plate 112.
The light guide plate 112 is a flat plate made of, for example, transparent acrylic resin and is formed by injection molding. The light guide plate 112 is disposed parallel to a display surface of the liquid crystal panel 120. The opposing surfaces of the light guide plate 112 and the liquid crystal panel 120 have substantially the same area.
To change the direction of light traveling in the light guide plate 112, a plurality of grooves 114, which are wedge-shaped in side view, are arranged in parallel on a front surface 112c of the light guide plate 112 to form a prismatic surface.
The long light guide bar 113 is bonded to an edge of the light guide plate 112, while the light source 115 is bonded to an end of the light guide bar 113. Although only one light source 115 is disposed at one end of the light guide bar 113 in the example shown in FIG. 9, two light sources may be disposed at respective ends of the light guide bar 113. An outer surface 113a (the surface opposite to the light guide plate 112) of the light guide bar 113 is provided with prismatic grooves (not shown) such that the direction of light traveling in the light guide bar 113 is changed by reflection thereat.
The light source 115 bonded to an end of the light guide bar 113 is a point source, such as a white light emitting diode (LED) and an organic electroluminescent (EL) device, and is designed to emit light toward the end surface of the light guide bar 113.
FIGS. 9 and 10 show light paths in the surface emitting device 110. As shown in FIG. 9, the light emitted by the light source 115 enters the light guide bar 113 through the end surface thereof. The direction of the light is then changed by the prismatic surface formed on the outer surface 113a of the light guide bar 113. The light is directed toward the light guide plate 112 and travels into it through a side surface 112a thereof. Subsequently, as shown in FIG. 10, the light propagating in the light guide plate 112 is reflected off the prismatic surface of the grooves 114, changes its direction, and emerges from the emitting surface (undersurface) of the light guide plate 112 toward the liquid crystal panel 120. The light thus illuminates the liquid crystal panel 120 on the backside (underside in FIG. 10) of the surface emitting device 110.
Since the light enters the light guide plate 112 through the entire bonding surface between the light guide plate 112 and the light guide bar 113, uniformity of the light on the emitting surface of the light guide plate 112 is improved.
The surface emitting device 110 including the above-described light source 115, the liquid crystal panel 120, and other necessary attachments are mounted in a molded case to form an LCD apparatus.
FIG. 11 shows a bonding structure between the light source 115 and the light guide bar 113. Normally, one end of a flexible printed circuit (FPC) 118 is bonded to the light source 115 for supplying power thereto, while the other end thereof is bonded with a bonding member, such as double-sided tape 117, to the light guide bar 113 or to the undersurface of a reflective panel 116 covering the light guide bar 113. Then, the surface emitting device together with the liquid crystal panel is mounted in a molded case 119. The light source 115 is thus secured to a bottom plate of the molded case 119 via the FPC 118. A displacement “d” between a centerline L1 of the light guide bar 113 and a centerline L2 of the light source 115 is caused by changes in thickness of the double-sided tape 117 and the FPC 118, or by the size of the LED chip constituting the light source 115. When the centerline L1 and the centerline L2 are not aligned, the amount of light entering the light guide from the light source is limited. This decreases the brightness, causes variations in brightness of the surface emitting device, and thus reduces the quality of a display screen of a reflective LCD apparatus.